This invention relates generally to a method and apparatus for rapidly filling small containers with an accurate weight of a product consisting of discrete pieces. The product can, for example, comprise beans, nuts, hard candy, fruit items, hardware items, etc.
Various systems are described in the prior art for rapidly filling small containers, e.g., one, three, or five pound, with discrete pieces of product, e.g., beans, nuts, hard candy, fruit items, hardware items, etc. Such systems typically include a product supply station which supplies the product onto a feeder subsystem, which in turn sequentially feeds pieces to a weighing station. A controller monitors the weight of the product at the weighing station and attempts to control the feeder subsystem and the discharge from the weighing station in order to achieve a precise discharge, by weight, into a product container.
Such systems traditionally use either a xe2x80x9clinear weighxe2x80x9d or a xe2x80x9ccombination weighxe2x80x9d procedure for filling the container with a correct product weight. In a typical linear weigh system, each successive cycle is comprised of two sequential phases, frequently referred to as a xe2x80x9cbulk feedxe2x80x9d phase and a xe2x80x9cdribble feedxe2x80x9d phase. During the bulk phase, a weighing cup is filled at high speed, e.g., by a conveyor, vibratory feeder, gravity gate, pump, etc., toward a target weight. When the cup weight reaches a first setpoint, the controller terminates the bulk phase high speed feed and switches to the dribble phase low speed feed. The cup weight thereafter increases at a lesser rate enabling the system to respond to a second setpoint to stop the product feed close to the target weight. Typically, the first setpoint is set at about 80% of the target weight in anticipation of overfill attributable to feed momentum (i.e., xe2x80x9cin-the-airxe2x80x9d) and component reaction time. In practice, with a first setpoint set at about 80% of target weight, the cup will typically weigh about 90-95% of target weight at the end of the bulk phase. The second setpoint is set to about 100% of target weight to cause the cup weight to just reach target weight when the dribble phase ends and the product pieces settle. It should be understood that the aforementioned setpoint numbers are exemplary only and depend in significant part on the reaction time of the system, the feed speeds, the incremental weight of each product piece, the geometry, settling time, etc. Thus it is generally necessary to xe2x80x9cfine tunexe2x80x9d a system to optimize accuracy and throughput.
Although the implementations of linear weigh systems can differ markedly, the cycle duration of such systems is comprised of the sum of the bulk phase duration and the dribble phase duration. Typically, the dribble phase, which may only involve about a few percent of the product weight, might consume up to 40% of the total cycle duration.
The present invention is directed to an enhanced filling/weighing system capable of exhibiting a greater system throughput than the aforedescribed linear systems. Enhanced throughput is achieved by configuring the system to concurrently perform bulk and dribble operations. More particularly, systems in accordance with the invention execute the bulk phase of cycle N+1 concurrent with the execution of the dribble phase of cycle N.
A preferred embodiment of the invention utilizes first and second weighing stages. The first stage includes a first top cup or container having an associated weighing device, e.g., a load cell. The second stage includes a second bottom cup or container having an associated weighing device, e.g., a load cell. A high speed bulk feed subsystem supplies product to the top cup. A low speed dribble feed subsystem supplies product to the lower cup, which can in fact comprise the end product container, e.g., a one pound capacity bag or box.
In operation, the bulk feed subsystem feeds product to the top cup at a high speed. The top cup fills to its first setpoint (plus overfill) once per cycle. When the system controller recognizes that the top cup weight has reached the first setpoint, it pauses the bulk feed, discharges the top cup into the bottom cup, starts the dribble feed into the bottom cup, and starts the next cycle of bulk feed into the top cup. Thus, the top cup fills at high speed during cycle N+1 concurrently with the bottom cup filling at low speed during cycle N. When the system controller recognizes that the bottom cup weight has reached the second setpoint, the dribble feed is interrupted and the content is transferred from the bottom cup to an end-proudct container. In a preferred system, the bottom cup comprises an end-product container so that after it is filled, it is moved and replaced by an empty end-product container.